The manufacturers of wireless mobile stations, especially cellular telephones, continually try to improve the reliability and performance of wireless products in order to create new markets and to expand existing markets. One very important performance characteristic of wireless mobile stations is power consumption. The users of wireless mobile stations value mobility and therefore place great importance on a long battery life. For example, cell phone users prefer to spend as little time as possible charging their cell phones and prefer cell phones that can operate for long durations before recharging. The same is true for users of laptop computers operating over a wireless network.
A wireless mobile station that has high power (i.e., high current) consumption can operate on battery power only for relatively short durations and must be recharged frequently. To extend battery life, manufacturers have worked both on improving battery capacity and on reducing the power consumption of wireless mobile stations. However, accurately determining the average time between recharges for a wireless mobile station is a complicated task due to fluctuations in power consumption caused by environmental conditions and the functions being performed by the mobile station.
Thus, accurate determination of power consumption (i.e., current drain) involves extensive testing of wireless mobile stations under varying conditions and while performing different types of tasks. These test are used to determine, among other things:
1) maximum battery life;
2) average battery life;
3) sleep mode power characteristics (e.g., wake-up time upon receiving a page);
4) standby mode, talk time; and
5) current drain during specific operations (e.g., sending e-mails, answering a call, and the like).
However, simply connecting a wireless mobile station to an external power cord and measuring the current drain in the power cord is an inaccurate method for determining true power consumption. This is because many wireless mobile stations operate differently (and therefore have a different current drain) when attached to an external power supply. When the wireless mobile station detects power from an external supply, the mobile station usually operates in a “high power” mode that provides better signal reception and transmission at the expense of higher power consumption.
However, when the external power source is removed and the mobile station operates only from its own battery, the mobile station may operate in a low power mode that saves power in a number of ways. For instance, a cell phone that is not in use may operate in a slotted mode of operation in which the cell phone cycles power one and off to some of its internal components. For instance, the cell phone may apply power to its receiver for one quarter of a second and may remove power to its receiver for three quarters of a second (25% duty cycle). The cell phone can only detect incoming calls during the time when power is applied to the receiver, but power consumption is reduced 75% in the receiver.
As a result, measuring current drain from an external power source does not provide an accurate assessment of power consumption because the cell phone does not operate in a low power mode. To compensate for this, some manufacturers have implemented intrusive means of measuring current consumption, such as altering the circuitry of the wireless mobile station to include test leads that can be connected to a suitable measuring device. However, such intrusive methods are not preferred because the required circuit alterations are of a delicate nature and are not robust. This makes field-testing a mobile station difficult. Also, such alterations would only be made on a small sample of wireless mobile stations, not all such devices. Thus, it is not useful for testing any mobile station at random.
Therefore, there is a need for improved apparatuses and methods for testing the power consumption (i.e., current drain) of a wireless mobile station. In particular, there is a need for a non-intrusive apparatus for performing power consumption tests in a wireless mobile station.